This invention relates to optical filters and, more particularly, to optical filters whose operation is based on varying the electro-optic properties of liquid crystal materials.
Liquid crystal optical filters are useful in a variety of applications of practical importance. In these applications, a liquid crystal filter provides an instrumentality for achieving electrically tunable wavelength selection.
In liquid crystal optical filters as heretofore proposed, the input light directed at the filter must be linearly polarized in a particular direction relative to the orientation of the liquid crystal molecules. Otherwise, the filter cannot be electrically tuned. In some applications, the polarization requirement imposed on the light directed at the filter is easily met. In other applications, however, such as in an optical fiber communication system wherein propagating light is generally elliptically polarized, such a requirement constitutes an undesirable and disadvantageous limitation.
Accordingly, efforts have continued which are aimed at trying to devise an electrically tunable liquid crystal filter whose operation would be insensitive to the polarization of input light. It was recognized that these efforts, if successful, could provide a compact low-power filter having operating requirements that would be viewed as advantageous in a variety of commercially important applications such as in optical fiber communication systems.